This invention relates in general to the manufacture of color television picture tubes and in particular, to an space-conservative apparatus with mechanical memory for holding and cataloging shadow masks associated with faceplates of the television picture tubes while the faceplates are being screened. Conventionally, a color television picture tube has a glass bulb including a funnel and a flanged faceplate sealed to the flared end of the funnel. The faceplate has a concave inner surface on which is deposited an electron excitable phosphor screen. A shadow mask of substantially the same size as the inner surface of the faceplate is fastened to the faceplate in close adjacency to the inner surface.
Conventionally, the phosphor screen is formed on the inner surface of the faceplate in the following manner. First a light-absorptive grill is formed on the inner surface of the faceplate. To form this grill a coating of polyvinyl alcohol is evenly applied to the inner surface after which the coating is exposed through the shadow mask by a light source in a lighthouse. Three exposures are made corresponding to the positions of the red, green and blue phosphor elements. The unexposed PVA is removed from the inner surface of the faceplate leaving a pattern of hardened elements. The inner surface is then coated with a light absorptive material. The hardened PVA elements are removed from the inner surface leaving a pattern of openings in the light-absorptive material. The inner surface is next coated with a slurry of green phosphor material. The same shadow mask is replaced on the faceplate and the faceplate and shadow mask are placed in a lighthouse where the green phosphor elements are exposed. The remaining unexposed green phosphor slurry is removed from the faceplate leaving a pattern of green phosphor elements in the proper openings in the grill on the faceplate inner surface. The shadow mask is removed from the faceplate and the blue phosphor slurry is applied to the inner surface. The same shadow mask is again replaced on the faceplate and the blue phosphor slurry is exposed on the lighthouse and the unexposed blue phosphor slurry is then removed from the inner surface. Likewise, the red phosphor slurry is applied and exposed. The inner surface of the faceplate then has the complete phosphor screen disposited on it. It is important to note that the faceplate and shadow mask must be joined together and separated a number of times, and that the shadow mask must be stored while the phosphor slurries are applied to the faceplate. Since a particular shadow mask was used to form a pattern of openings on the inner surface of the faceplate in the grill, it is necessary due to the close tolerances involved to replace the same shadow mask onto the faceplate after the grill has been formed as well as after the phosphor slurries have been applied. This necessitates that a one-to-one correspondence between each faceplate and shadow mask be maintained at all times. Also the shadow mask being fragile must be protected against excessive handling and impurities while it is detached from the faceplate and awaiting reassembly.
Conventionally, the faceplate of a color television picture tube moves through a phosphor coating machine where the phosphor slurry is applied to the inner surface in various steps. While the faceplate moves through the phosphor coating machine, the corresponding shadow mask rides or hangs from a conveyor belt above the faceplate either within the machine or above the machine. Therefore, the faceplate and corresponding shadow mask are always together and no confusion can come about in attaching a shadow mask to its proper faceplate. Several disadvantages are present in this type of system. The mask may be damaged or its tiny perforations clogged by its being in close proximity to the machinery which coats the faceplate with the phosphor slurry. In addition, the conveyor belt carrying the shadow mask requires a significant amount of space within the factory and also is expensive.
U.S. Pat. No. 3,912,963 issued to Sedivy, and assigned to the same assignee as the present application, discloses a unique type of faceplate and shadow mask. The faceplate has no flange and the shadow mask is supported directly on the faceplate by a mask suspension system comprising four mask suspension devices, one located at each corner of the mask. This permits the mask to be quickly and precisely mounted on the faceplate. This unique type of shadow mask has no frame and is flexible so that it may conform to any minor deviations in the inner surface of the faceplate. As a result, however, the shadow mask is delicated and easily damaged by excessive handling or exposure to impurities in the atmosphere. The novel apparatus of this invention for use in holding and cataloging the shadow masks while the faceplates are being screened is applicable to the standard type of shadow mask as well as the unique time of frameless shadow mask described above.